This invention relates to a system for improving the flow characteristics of gases fed from ducts into a combustion chamber of an industrial gas-fired system, particularly a coke oven, which includes regenerative or recuperative recovery of heat from waste gases of the combustion process. More particularly, the present invention relates to such a system for conducting heated gases into heating flues from ducts communicating with the outlet of a heat exchanger; such gases comprising air when rich gas is used for the combustion process or air and lean gas when lean gas is used for the combustion process.
An industrial gas-fired system using regenerative or recuperative recovery of heat from waste gases, particularly when rich gas is used to fire the system, is subject to constructional constraints due to the physical arrangement of the ducts required to convey the preheated combustion media from the regenerator or recuperator outlets to the combustion chambers. Because of these constraints, it is difficult to obtain uniform combustion with a uniform elongated flame. For example, the ducts in coke oven batteries are at a relatively acute angle to the horizontal because of structural requirements in the arrangement of regenerator cells depending, of course, on the heating system. The ducts terminate with a relatively short vertical duct portion leading to the heating flue. Usually, the length of the vertical duct portion is insufficient to obtain a uniform flow of gases in the cross section of the gas stream. Moreover, the length of the vertical duct portion is insufficient to obtain guiding for the gas stream such that the stream is vertical when entering the flue. Indeed, tests on models have shown that a stream of preheated combustion air drifts to a relatively considerable extent from the vertical when it enters the base of the heating flue. This results in a strong turbulence in the lower part of the heating flue which is intensified by a horizontal velocity component in the gas stream because of a sudden increase to the diameter of the stream upon entering the heating flue. An intensive spontaneous mixing of the combustion gas and the air occurs which brings about an excessive local flame temperature. In many industrial gas-fired systems, such an excessive flame temperature, even if it is locally limited, increases the formation of NO.sub.x. Tests on the flow models have also shown that the drift of the flowing combustion air in the gas stream continues to higher regions of the flues, thus preventing a uniform vertical temperature distribution.